1. Field of the Invention
The present invention relates to an electronic component including a piezoelectric element provided with vibrating part which generates a vibrational wave on a substrate and a manufacturing method thereof.
2. Description of the Related Art
As an example of a piezoelectric element, there is a surface acoustic wave (SAW) element. This SAW element is an element which uses a surface acoustic wave propagating along the surface of a solid body and, for example, has a structure in which plural comb electrodes making pairs called ITDs are provided on one face of a piezoelectric substrate. When an electrical signal is applied to comb electrodes making one pair, an electric field is generated around these comb electrodes, a SAW generated by excitation of these comb electrodes propagates along the surface of the piezoelectric substrate to excite comb electrodes making another pair, and the SAW is converted into an electrical signal in these comb electrodes. For example, a SAW filter, for example, as one of the SAW elements obtains a filtering function using such a conversion, and it is widely used, for example, for a portable electronic device.
The SAW element needs to secure an active region as a space for the comb electrodes to vibrate and for the SAW to propagate, and in order to prevent the comb electrodes from being corroded by moisture and damaged by impact, the active region needs to be sealed hermetically. Therefore, the SAW element is sometimes manufactured as one electronic component (SAW device) by being mounted on a printed circuit substrate and provided with a sealing member so that the active region is hermetically sealed. Various studies on materials used as the sealing member and methods for performing this sealing have been so far performed.
For example, Patent Document 1 and Patent Document 2 each disclose a SAW device in which a dam made of a photosensitive material and preventing a resin from flowing into an active region is provided on a functional face of a piezoelectric substrate of a SAW filter so as to surround comb electrodes, a paste resin is supplied so as to cover the outer periphery of the dam and the periphery of the piezoelectric substrate, then this resin is cured to become an exterior resin, and the active region is sealed by being surrounded with the exterior resin and the dam.
Patent Document 3 discloses that a first metal layer is provided on a functional face of a piezoelectric substrate of a SAW filter so as to surround input/output electrodes and comb electrodes, while an annular second metal layer is provided at a position corresponding to the first metal layer on a mounting face of a printed circuit substrate, and solder bumps on substrate electrodes on the printed circuit substrate side and a solder layer on the second metal layer on the printed circuit substrate side are formed, respectively, by printing. Cream solder is used for these solder bumps and solder layer. After the input/output electrodes are temporarily fixed onto the substrate electrodes via the solder bumps, for example, by ultrasonic thermocompression bonding, by carrying the piezoelectric substrate and the printed circuit substrate through a reflow furnace, the input/output electrodes of the SAW filter and the substrate electrodes of the printed circuit substrate are electrically connected by melting the solder bumps, and simultaneously the first metal layer and the second metal layer are bonded by melting the solder layer, thereby sealing an active region.
Patent Document 4 discloses a SAW device in which a first metal layer is provided on the entire peripheral side face of a piezoelectric substrate of a SAW filter, while a second metal layer is provided on a mounting face of a printed circuit substrate so as to surround a projection region of the piezoelectric substrate onto the mounting face, the SAW filter and the printed circuit substrate are electrically connected by bonding input/output electrodes on the piezoelectric substrate side and substrate electrodes on the printed circuit substrate side each via a solder material, and then the solder material is further supplied in a cylindrical shape so as to span the first metal layer and the second metal layer to thereby seal an active region.
Patent Document 5 discloses a SAW device in which an annular first metal layer is provided on a functional face of a piezoelectric substrate of a SAW filter so as to surround input/output electrodes and comb electrodes, while a second metal layer is provided at a position corresponding to the first metal layer on a mounting face of a printed circuit substrate, and by pressurizing the piezoelectric substrate with respect to the printed circuit substrate, the input/output electrodes of the piezoelectric substrate and substrate electrodes of the printed circuit substrate are thermocompression-bonded and electrically connected, and simultaneously the first metal layer and the second metal layer are thermocompression-bonded to thereby seal an active region.
However, in the SAW devices described in Patent Document 1 and Patent Document 2, the dam and the exterior resin sealing the active region are both composed of an organic substance. Since the organic substance generally has higher moisture permeability than inorganic substances such as metal, there is a possibility that corrosion of the comb electrode cannot be sufficiently suppressed. In these SAW devices, for example, it is thought to suppress the corrosion by forming a protective film made of SiO2 (silicon oxide) on the comb electrode or increasing the thickness of the exterior resin, but when the protective film is formed, this protective film influences the vibration of the comb electrode, which may cause a degradation in the electrical property of the SAW filter. Moreover, when the thickness of the exterior resin is increased, these SAW devices may possibly increase in size.
In the SAW device described in Patent Document 3, using the cream solder as the bumps for connecting the input/output electrodes and the solder layer for sealing, the connection between the electrodes and sealing are performed simultaneously by melting the cream solder, and therefore the older bumps wet to the respective electrodes when melted, so that the occupied area of the solder bumps becomes larger. As a result, a reduction in the size of the SAW device may possibly be hindered.
Moreover, for example, in this Patent Document 3, it is suggested that Sn (tin)—Sb (antimony)-based and Sn—Ag (silver)-based solders are used as the solder materials, but since the solidus temperatures of these solder materials are generally low, for example, from about 218° C. to about 245° C., there is a possibility that when the SAW device is mounted on another electronic device by reflowing, the solder bumps and the solder layer are melted again by heat of the reflow furnace, the electrical connection between the SAW filter and the printed circuit substrate is damaged, and that the solder layer is not uniformly fixed to respective portions when solidified after reflowing, so that the hemeticity of the active region lowers.
Further, in the SAW device described in Patent Document 4, the first metal layer is provided on the entire peripheral side face of the piezoelectric substrate of the SAW filter, but considering that the SAW filter is generally manufactured by being cut to have a predetermined size after comb electrodes are formed on the piezoelectric substrate and that the thickness of one piezoelectric substrate is, for example, from about 0.3 mm to about 0.5 mm, it is technically difficult to provide the metal layer on the entire peripheral side face of the piezoelectric substrate as described above, and even if it can be realized, it may cost a lot.
Furthermore, in the above SAW device, for sealing, the solder is supplied in a cylindrical shape so as to spread from the peripheral side face of the piezoelectric substrate of the SAW filter toward the outside on the printed circuit substrate, so that, for example, compared with when a metal layer is mounted on a functional face of a SAW filter and solder is supplied to the metal layer for sealing as in the SAW device described in Patent Document 3, the region to which the solder is supplied on the mounting substrate becomes larger. This may cause an increase in the size of the SAW device.
Moreover, in the SAW device described in Patent Document 5, the thermocompression bonding between the first metal layer and the second metal layer is performed simultaneously with the thermocompression bonding between the input/output electrodes and the substrate electrodes, but the printed circuit substrate is usually composed of ceramics or the like and therefore sometimes warps, which makes it difficult to uniformly thermocompression-bonding the electrodes and the metal layers, and raises a concern about problems such as poor connection and non-ensuring of hermeticity.
From the above circumstances, a SAW device excellent in moisture resistance and productivity capable of suppressing an influence on the electrical connection between electrodes and the hermeticity of the sealed region when it is heated for mounting on another electronic component, and further suppressing an increase in size has been demanded.
(Patent Document 1)
Japanese Patent Application Laid-open No. Hei 8-316778 (Paragraph numbers 0009, 0010 and FIG. 2)
(Patent Document 2)
Japanese Patent Application Laid-open No. 2004-64732 (Paragraph number 0024 and FIG. 1)
(Patent Document 3)
Japanese Patent Application Laid-open No. 2004-153579 (Paragraph numbers 0045 to 0047, 0061, 0062 and FIG. 2)
(Patent Document 4)
Japanese Patent Application Laid-open No. Hei 9-289429 (Paragraph number 0010 and FIG. 1)
(Patent Document 5)
Japanese Patent Application Laid-open No. 2004-214469 (Paragraph number 0040 and FIG. 1)